A conventional structure for engaging a bolt has been disclosed in the Japanese Utility Model Application Laid Open Number 1-118216. In this description, clips including the bolt engaging structure are used for fixing wire harnesses for vehicles.
FIGS. 1A and 1B are respectively a plan view and a side elevational view of a clip which is similar to the clip mentioned above. As shown in FIGS. 1A and 1B, a boss section 3 extends from a sheet of plate 2 with which a wire harness W is securely bound by a roll of tape T. This boss section 3 has a cylindrical wall which defines a hole 5 for receiving a stud bolt 4 therein as shown in FIGS. 2 and 3. In this hole 5, flexible engaging portions 6 are provided. These engaging portions 6, while slanting inwardly, extend from the cylindrical wall of the boss section 3. Namely, these engaging portions 6 substantially extend in a first direction A in which the boss section 3 may be pulled off of the bolt. Further, the engaging portion 6 includes an engaging click 7 which is positioned in a distal part of the engaging portion 6 so as to engage with the roots of the threads of the bolt 4.
In order to engage the clip 1 with the threads of the bolt 4, the hole 5 of the clip 1 is abutted against a thread portion M of the bolt 4 and then the boss section 3 is pressed relative to the bolt 4 as shown in FIG. 3. The engaging portions 6, while being pressed by the thread portion M of the bolt 4, flexes slightly toward the cylindrical wall of the boss section 3 to allow the bolt 4 to be received inside the boss section 3. After this step, the engaging clicks 7 of the engaging portion 6 become engaged with a root of threads of the bolt 4 to prevent the bolt 4 from being slipped out of the boss section 3.
In this bolt engaging structure described above, if a pulling force F along the first direction A is applied to the clip 1 as shown in FIG. 4, the engaging portions 6 are forced to be bent toward a second direction B which is opposite to the first direction A and in which the clip 1 is pressed to receive the bolt 4. In other words, the engaging portions 6 are forced to be bent toward the second direction B which is opposite to the direction in which the engaging portions 6 substantially extend. Thus, if the pulling force F is applied to the clip 1, it may happen that the engaging portions 6, while being buckled, become disengaged with the root of threads 4a and are pulled off of the bolt 4.
In order to prevent the clip 1 from being pulled off of the bolt 4, it may be thought that the engaging portions 6 should be thickened. However, if the engaging portion 6 is thickened, a stronger force to press the clip 1 relative to the bolt 4 is needed when the clip 6 receives the bolt 4. Accordingly, thickening the engaging portions 6 is undesirable. Thus, up to now, it was difficult to provide a clip with a sufficient force for preventing the clip from being pulled off of the bolt.
The Japanese Utility Model Application Laid Open Number 1-163277 discloses another type of bolt engaging structure. As shown in FIG. 5A, in this bolt engaging structure which is employed in a clip 1', an engaging portion 6' has a pair of engaging clicks 7a, 7b. In this clip 1', since the two engaging clicks 7a, 7b simultaneously engage with roots of threads 4a of the bolt 4, while the bolt 4 is being received within the clip 1', a stronger force is needed to press the clip 1' than a pressing force to press a clip having a single engaging click. Furthermore, if a force is applied to the engaging click 7a which is positioned in the distal part of the engaging portion 6', since the engaging click 7a is far from the base part of the engaging portion 6', there is a fear that the engaging clicks 7a may disengage with the roots of threads and the clip 1' may be pulled off of the bolt 4. Further, stress may easily occur between the engaging clicks 7a and 7b, whereby the engaging click 7a may easily be broken.